calibration of RTC for SAMA5D2

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dinhhung
Posts: 1
Joined: Wed Oct 25, 2017 10:03 am

calibration of RTC for SAMA5D2

Wed Oct 25, 2017 12:18 pm

Hi,

I have a problem with drift (over 11%) of RTC by using internal RC oscillator. But the calibration of the RTC is difficult.
Because (datasheet of SAMA5D2 Series):
- The 64kHz RC oscillator frequency can be between 40kHz and 90kHz.
- The RTC clock calibration circuitry allows positive or negative correction in a range of 1.5 ppm to 1950 ppm.

How can I calibrate the RTC accurately?

thanks
blue_z
Location: USA
Posts: 1738
Joined: Thu Apr 19, 2007 10:15 pm

Re: calibration of RTC for SAMA5D2

Wed Oct 25, 2017 10:02 pm

dinhhung wrote:How can I calibrate the RTC accurately?
You might be able to calibrate it, but maintaining accuracy is another (long-standing) issue.
The Atmel app note AT03155: Real-Time-Clock Calibration and Compensation describes the accuracy problem and how to use the calibration feature of the RTC. The document is written for the SAM3/4 series, but the RTC in the SAMA5D2 has the same calibration feature.

If you insist on using the less-accurate 64kHz RC oscillator as the SCLK source, then study this other app note, Using a Real-time Timer with Non-calibrated RC Oscillator as a Real-time Clock.

Regards

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